Although the direct effects of nicotine on the brain are presumably responsible for the major reinforcing effects of cigarette smoking, peripheral actions of tobacco smoke, including those of nicotine, may account for important secondary reinforcing properties of cigarette smoking. This proposal deals with the subjective reactions to the interaction of cigarette smoke with the linings and receptors of the mouth, throat, and respiratory tract. Non-nicotine components of smoke, broadly known as tar, have been shown by us to play a role in smoking and we will study the reinforcing effects of this substance. The result should throw further light on the process of smoking and help to engineer a more rational approach to the control of the habit.